There are a number of products in various industries, including automotive, office and home furnishings, construction, and others; that require materials having a z-direction thickness to provide both structural strength as well as thermal, sound insulation, aesthetic, and/or other performance features. In many of these applications it is also required that the material be thermoformable to a specified shape and rigidity. In the automotive industry these products often are used for shielding applications such as noise and thermal barriers in automotive hood liners, underbody shields, firewall barriers, and trunk liners.
Composite materials used in automotive applications like package shelves, door panels or headliners are often produced via cold pressing structural nonwoven composite layers bound by a thermoplastic binder fiber to a decorative layer. For this, the composite layer used as substrate bound by thermoplastic binder is heated by means of infrared radiation to a temperature between 180° C. and 200° C., placed in a cold molding press together with a decorative layer, and cold pressed with the decorative layer. The composite layer can comprise by way of example polypropylene or polyester core-sheath binder fibers, and use natural fibers, glass or carbon fibers as the reinforcing fibers.
A disadvantage of these purely thermoplastic systems is that the weight per unit area of the composite substrate tends to be high in order to achieve the mechanical properties (modulus of elasticity and tensile modulus) required. In addition, the composite may have dimensional stability issues when the operating temperature exceeds the softening point of the thermoplastic binder.
As an alternative to this, it is possible to use composite layers bound by a thermosetting resin system, for example bound by an epoxy resin. Here, a moldable prepreg is produced and then molded via hot pressing in a heated mold.
It is the objective of this invention to provide a process which is simple to carry out for producing structural nonwoven composite materials with an A-surface face layer in one-step without the need for an adhesive or a separate lamination step. In addition, the invention uses a combination of thermoplastic binder fiber and a thermosetting resin to improve the mechanical properties of the composite and the dimensional stability at elevated temperatures. In one embodiment, thermoplastic binder fibers with grafted functional groups are used to improve the bond strength within the fiber network and improves the mechanical properties.